Magnetic devices such as inductors are often used in circuit design for electronic devices (e.g., power modules) in which energy is stored in a magnetic field surrounding an electrically conductive element such as a coil of copper wire. To produce an inductor that can store a useful amount of energy for a given size and a given current level, a number of electrically conductive turns or wires are formed around a magnetic structure or core such as a layer of magnetic material. The magnetic field is enhanced by the permeability of the magnetic material and by the presence of the multiple conductive turns. As the size of electronic devices has been reduced by using integrated circuits and printed wiring boards with surface-mount assembly techniques, the size of inductors has not, to date, decreased proportionately. Thus, the size of magnetic structures generally dominates the size of present electronic power modules.
Substantial progress has been made in recent years in integrating control circuits including operational amplifiers, comparators, and passive circuit elements, with active elements such as field-effect transistors. An area that has been more challenging is to produce a power module that includes larger passive elements, such as inductors, that are difficult to include in an integrated circuit, with an active element that may include control circuit elements and passive elements such as resistors on the same die. The integration of larger passive elements such as inductors with an active element would enable the production of very compact power modules.
A characteristic that affects broad market acceptance of a power module is its physical size, which introduces thermal design challenges. A continuing area affecting the design of a compact power module that requires further progress is the ability to dissipate the heat produced by passive circuit elements in a compact physical structure, as well as the heat produced by active elements. The dissipation of heat from these sources is performed in a challenging external thermal environment without compromising a power rating of the power module.
A number of approaches have been used in the past to reduce the size of a power module. For instance, U.S. Pat. No. 5,574,420 entitled “Low Profile Surface Mounted Magnetic Devices and Components Therefor,” to Roy, et al., issued Nov. 12, 1996, which is incorporated herein by reference, discloses a magnetic device that forms conductive pathways in a body of magnetic material, adds windings by inserting staple-like conductive piece parts through apertures in the body, and solders the staples to a patterned printed wiring board placed below a ceramic magnetic bar to complete the winding structure. Each of the magnetic devices disclosed in the aforementioned references suffers from a current limitation therefor, which is an impractical design and manufacturing approach for a mass market. The aforementioned magnetic devices also provide inadequate heat dissipation capability or reduction in the size thereof.
Another approach is disclosed in a technical specification from Ericsson designated “EN/LZT 146 318 R1C,” Sep. 2006 for PMF 8000 series point of load (“POL”) regulators, which is incorporated herein by reference. As illustrated on the first page of the technical specification, the PMF 8000 series POL regulators provides a magnetic component of large size and discrete implementation without any heat removal capability causing an inadequate ability to shrink the size of the device or remove heat therefrom. Another approach is disclosed in U.S. Pat. No. 6,366,486 entitled “Power Supply Device for Enhancing Heat-Dissipating Effect,” to Chen, et al. (“Chen”), issued Apr. 2, 2002, which is incorporated herein by reference. A package of Chen includes a printed circuit board, a transformer, an inductor having an inductive winding, a metal strip electrically connected to the inductive winding, and a converter electrically connected to the metal strip and covered by the metal strip. The aforementioned magnetic device also provides inadequate heat dissipation capability or reduction in the size of a power module.
Thus, the designs for power modules of the past are inadequate to produce a sufficiently miniaturized, high-density device with a substantial power rating. The power modules should be more compact than presently achievable designs. The design of power modules is inadequately served by these aforementioned limitations. In addition, a power module integrable with manufacturing processes of a commensurate end product would provide substantial cost savings therefor.
Accordingly, what is needed in the art is a power module, and related method of forming the same, that can meet the more stringent requirements of present applications such as compactness, efficiency and high power density, while being manufacturable at high volume and with lower cost than is achieved with conventional design approaches.